15 years after the 'York' systematic scientific review by the NHS Centre for Reviews and Dissemination cast serious doubt on the evidence surrounding water fluoridation, a follow-up review by the Cochrane Collaboration published in April 2015 has come to similar conclusions.

Cochrane found that fluoridation led to around a 15% increase in children with no decay in their teeth. While confident about this finding in children 40-plus years ago when the majority of studies were conducted, they could not be certain about the extent if any to which this change in the percentage of children affected holds true today. They found "very little contemporary [i.e. up-to-date] evidence", a high risk of bias within 97% of the studies admitted, and questionable applicability of fluoridation to modern life where fluoridated toothpaste is common, dietary patterns are different, and caries incidence is much lower. They found insufficient evidence around any effect of fluoridation on adults, or around disparities in caries across socio-economic groups. There was an association between fluoride level and dental fluorosis: at a level of 1 part per million, fluorosis may be found in up to 47% of a population and in an unsightly form in up to 15%. Reviewers did not address other questions about harm or safety, or ethical or environmental arguments.

The Cochrane systematic review provides the most authoritative evidence to date on the effects of fluoridated water, currently delivered at 1 ppm to over 5 million people in England.